BACTERIA SIGNALING AND BEHAVIOR MECHANISMS Day 3 Pfeffer capillary assay was modified to permit a quantitative study of chemotaxis. This involved counting bacteria that entered the capillary. Outline: 1) With the Pfeffer essay he used liver extract and noticed the bacteria were congregating around the mouth of the capillary. This led him to believe something was attracting them there. 2) Defined chemicals were tested as attractants. 3) Attractants could be metabolized but metabolism was not necessary. 4) Genetic evidence for external receptors for attractants. 5) Biochemical evidence for structural recognition of attractant by receptors and for different classes of receptors 6) First molecular scheme for how chemotaxis might work. • Questions: 1— what are the bacteria attracted to? 2— what is the mechanism of attraction? 3— is the response to the attractant itself or its metabolic product or the energy produced? 4— are the bacteria entering the capillary simply because they are hungry? 5— how many receptors are involved in attraction of the bacteria? Method: Julias used the same assay, but he quantitated it. He allowed the bacteria to enter the capillary, then took it out and plated them, and then counted the PFU’s that formed. Main discoveries: 1) Readily metabolized chemicals are not necessarily attractants. 2) First products of metabolism do not attract. 3) Mutants that cannot metabolize a chemical are still attracted to it. 4) Metabolized chemicals do not block attractants. 5) Structurally related compounds compete. 6) Mutants that fail to do chemotaxis can still be metabolized 7) Mutants that fail to transport can still do chemotaxis. Results: 1) The bacteria were attracted to glucose but not attracted to glycerol. a.

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